Brake safety redundancy is an important requisite in a variety of contexts. For example, in a gamma camera system used for molecular imaging, some motion axes can be moved freely by gravitational force. A motion controller is an electronics assembly sub system that controls all of the gamma camera motion axes. Examples of gamma camera motion axes are camera rotation, camera radial movement and patient bed up/down movement. Each motion axis generally includes an electric motor with mechanical gearing, electric brake(s), position feedback sensors (i.e. optical encoder, potentiometer) and travel limit sensors.
The motion controller performs a closed-loop control on each motion axis in order to move the camera to the desired position at the desired velocity. The motion controller also controls the electrical brake for a motion axis that requires position holding when power is not applied to the electric motor, thereby to prevent free movement by gravitational force. For such axis, two brakes are normally provided redundantly for safety. The brakes are used to hold their positions when the motion controller is off, to stop motion when the system loses power, or in a system emergency stop condition. In normal operation, both brakes are controlled to release or engage simultaneously. If one of the brakes fails in its release condition, the motion axis loses its brake safety redundancy without detection of the failure.
In order to reduce the probability of failure, preventive maintenance is routinely performed. During preventive maintenance, each brake is tested independently to verify that it can hold the load against gravity by itself. For an axis motion controller that has two independent brake controller/drivers, the test can be done automatically. However, if the motion controller has only one brake controller/driver, the test requires service personnel to perform manual tasks of connecting and disconnecting each brake during the test.
FIG. 1 is a block diagram of conventional brake redundancy testing with a single brake controller/driver. Electromechanical redundant brakes 10 and 12 are each engaged with an axis 14 of motion device 15 when no voltage is applied to energize associated brake coils 11 and 13. While the motion device 15 is exemplified as a diagnostic camera device for simplicity, the motion device is representative of any of a variety of equipment for which redundant brake capability is desirable. Brake coils 11 and 13 are physically connected in parallel at nodes 16 and 18 in motion distributor board 20.
Motion electronics base 22 comprises input terminals for coupling to supply lines V0 and ground. The motion electronics base directly connects the ground terminal to node 18 and connects the V0 terminal to node 16 through supply switch 24 and brake driver switch 26. Switches 24 and 26 may be electronic switches under control of motion controller 30. Motion electronic base 22, for example, may correspond to the controller for the Siemens e.cam series cameras. The motion controller 30 contains various subsystems for operation of the motion device 15, including control of axis rotation, radial drive, patient handler in/out and up/down axes, left/right gantry motion, motion detection, emergency stop controls, and brake testing. This functionality is schematically indicated by the coupling of the motion controller 30 to the device 15 by link 32.
Brakes 10 and 12 are released from the axis 14 when supply switch 24 and brake driver 26 are activated by the motion controller 30 to apply input power to brake coils 11 and 13. When the brake driver switch 26 is turned off, both brakes are engaged. In order to test brake redundancy during a preventive maintenance test, a service technician must gain access to the motion distributor board 20 to manually disconnect one of the brakes from the nodes 16 and 18 in order to test only one brake function at a time. After the first brake is tested, it must be disconnected and the other brake connected, these functions also manually performed. Removal of system covers to gain access to the brakes for the connections and disconnections can be time consuming.
A need thus exists for attaining brake redundancy testing in a single controller system that does not require manual intervention by service personnel and that provides the redundancy testing without delay.